I've owned or looked through about 12 of these scopesI have found about 1/2 are horrible optically, 25% are acceptable and 25% are corrected wonderfully. The one I currently have is an example of the excellent ones,I got terrifically lucky buying it on ebay sight unseen for a little over $100.00 USA currency.the mounts on these are only surpassed by Questar, the Meade 2045 comes close.there are a few versions of these and this opens the opportunity to come closer to good optics.the earlier ones have a gold band around the top of the tube assembly. These are usually the poorest quality, especially in the spotter variation, B&L retooled and re-released the last version as the "pro" version, 6" pro and the 8" was renamed 8001, a semi gloss textured aluminum tube without the gold band.The other pro I had was not quite as good as this one optically with a llittle "dog ear" abberation ( a little fuzzyness on one spot in the optics.I get a tight aery disc with a symetrical defraction ring with a fainter second one. a faint misting of light around the object keeps this from being a 10, no multicoatings on the correctorThis came from and estate sale and the guy died before selling this scope...I am very interested in finding a good 6" Pro and would be willing to give a substantial price for an above ave. example..also interested in any Dynamax 8/6/ or B&L 8001 or 8000.ldbeachtec@hotmail.com

This scope is a typical SCT from what i have seen. Mine performs on par with what you would expect a C8 to do with aperture in consideration. The mount is steady, it is easier to use than the etx 90. The optics seem good for a C8 but i would like to replace the diagonal, but can't because the threads aren't standard with meade and celestron. It is good for a travel scope but not as a primary. I would want more aperture for a primary scope. If you can get one for 250 or less not a bad deal.

I bought mine used with a cracked corrector plate (!!!) on EBay for $50. Fork mount and drive base work fine and are in pristine condition. I replaced the corrector plate (myself!!!) with a used Tokina 105mm multi-coated UV filter (!!!) as I was desperately trying to restore it to somewhat usable order. I figured that I would have nothing to lose if the "modification" did not work. The view turned out OK (!!!) when I pointed the scope at Mars last week - obvious undercorrection but nevertheless the Martian disk is bright and quite contrasty. After tweaking with the collimation I was able to use over 100X with acceptable results. A surprise considering the total cost ($65.00) I spent and the total lack of technical considerations that had gone into the "optical transplantation". As it turns out my little Criterion 4000 now performs pretty "healthy" in comparison to several other quality 80mm achromats my friend owns.

I have had my 4000 for 25 years. While the views were not ever really "bad" , I was never completely happy with the optical performance compared with my other scopes. The optics always suffered from some astigmatism and yielded a broken trefoil first diffraction ring and a small but vaguely triangular in focus star image when examining a star at very high magnification. While views of the moon were OK at 175-180X , planetary performance lacked "bite" at anything over 120x. I realize now that best collimation was not curing an actual mechanical misalignment (tilting) of the primary with respect to the secondary. Performing normal collimation would improve the view but at the same time induce other aberrations. It was a balancing act compromise between astigmatism and coma This loss of performance however was not detectable doing a 133 line ronchi test. The optics displayed nice straight relatively smooth lines even with only 3-4 lines intersecting. After all these years I have finally fixed this scope and it now performs admirably. I removed the secondary mirror from the scope (leaving the secondary holder in place), and placed a laser collimator in the visual back where an eyepiece would go. The secondary holder on the B&L 4000 has a threaded hole in the exact center and shining a laser beam verified the laser beam was not hitting the hole. I carefully centered the holder (there is about 1/16" movement available) until the beam was centered on the hole. I then put everything back togeter and collimated on Polaris using magnifications of up to 300x. The scope is now an excellent performer with nice round airy dick in focus with a clean concentric first diffraction ring. Images of the moon can now be pushed to 240x and still decent. For the first time in 25 years the scope now shows Cassini's division plainly visible instead of a strong suspicion previously. Contrast is greatly improved and gone is the fog like haze that used to surround brighter objects. bhxc

These scopes were literally shoved out the door during the Halleys' Comet era with very poor quality control in an effort to keep up with demand. The result is a telescope that is constructed of decent quality materials but suffers from mediocre optics and poor assembly. Getting a good one is a crap shoot. Avoid this scope unless you can test the optics. Most I have seen never rose above the level of fair, with most bordering on defective. B&L never got their act together until the 8001 came out a year or two before B&L quit making SCTs.. It is a shame the 4000 suffered from sloppy quality control. It could have been a very nice little scope.

I've had my scope since about 1988. I five eyepieces and a solar filter--this scope has never disappointed! Jupiter and Saturn are easy and the moon (and sunspot) views are stunning! Switched from 35mm to digital quite a while ago and am now trying to resurrect this scope for digital (have the t-adapter and now am trying to hook up a Nikon Coolpix 8400 to it). Rediscovering astro-photography: priceless!

i've had one since the mid 80's, not bad for a little scope. views were great with the supplied eyepieces, 30mm and 18mm. not too hot a high power. 200x was never an option.tracked reasonably well, hard to accurately polar align, but for casual viewing, it's not a problem. finderscope is about worthless. it's 4x and hard to look through.a telrad helps tremendously. check balance before "sticking" the telrad on as this is a small scope and a few accessories can take it out of balance in a hurry. very portable and best with a field tripod and wedge. table top use would need a rock solid base.

Some people think these scopes are ok but mine is mediocre...at least compared to a truly good telescope. Pinched optics, mild astigmatism 1/3 wave undercorrection rough optical figure. In other words typical of mass produced schmidt cassegrains of the Halleys comet era. Gives a tri-lobbed bunched diffraction ring with a spurious disk at high power that is not perfectly round but vaguely a rounded corner triangle. (a sign of pinched optics, I can't unpinch it) The bright first bright diffraction ring often hides close unequal mag binary companions that should be visable with a 4 inch. Planetary contrast mediocre...my 60mmm Sears/towa refractor and an Edmund 60mmm Rank achromat blows it away on Jupiter and Saturn and also on the Double Double. Not recommended if you want it for nice planetary views, but OK for viewing stars, moon, sun (with aperture filter)or casual observing with easy portability. The sope does have a stable mount with robust fork arms. If mounted on a decent tripod it is quite steady.